Stable electrochromic module

ABSTRACT

An electrochromic module including a first substrate and a second substrate is provided in which the first and/or the second substrate are/is electrically conductive or are/is equipped with an electrically conductive coating. An electrochromic polymer coating is arranged on the substrate or the conductive coating, an ion storage layer is arranged on the substrate or the conductive coating, and a polymer gel electrolyte is disposed in an electrically in-series connection between the electrochromic coating and the ion storage layer. The electrochromic polymer is a polymer of tetraarylbenzidine and (hetero)aromatic diol, which can be switched reversibly between redox states in a voltage-controlled manner. The condensation polymer is colorless in one redox state and colored in at least two redox states. The inventive modules achieve a large number of switching cycles without an appreciable decrease in the electrochromic properties, a high electrochromic contrast and a high electrochromic efficiency with effective switching kinetics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is being filed under Rule 1.371 as a National StageApplication of pending International Application No. PCT/EP2012/000932filed Mar. 2, 2012, which claims priority to German Patent ApplicationNo. 10 2011 013 132.9, filed Mar. 4, 2011. Both InternationalApplication No. PCT/EP2012/000932 and German Patent Application No. 102011 013 132.9 are hereby incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

The invention relates to an electrochromic module comprising a firstsubstrate, a second substrate, the first and/or second substrate beingelectrically conductive or having been provided with, respectively, afirst electrically conductive coating or with a second electricallyconductive coating, a coating of an electrochromic polymer disposed onthe first substrate or the first conductive coating, an ion storagelayer disposed on the second substrate or the second conductive coatingand an electrically series-connected electrolyte disposed between theelectrochromic coating and the ion storage layer.

BACKGROUND OF THE INVENTION

It is a feature of the inventive electrochromic module that it can beswitched reversibly under voltage control between more than two colorstates and has, after a large number of switching cycles without anysignificant decline in the electrochromic properties, a highelectrochromic contrast and a high electrochromic efficiency with rapidswitching kinetics, and is additionally leak-proof.

The electrochromic polymer used is an essentially linear condensationpolymer formed from a substituted tetraphenylbenzidine and a(hetero)arylenebisphenylmethanol of the general structural formula (I),(II), (III) or (IV)

where R1 and R2 are the same or different and are each an alkoxy group,a halogen atom, a cyano group or a hydrocarbyl radical having 1-10carbon atoms, preferably an alkyl group, an allyl group or a vinylgroup, and R3 is a divalent radical of an optionally substitutedaromatic or heteroaromatic compound, preferably of benzene, ahydroquinone dialkyl ether, diphenyl ether, biphenyl or naphthalene.

Electrochromic modules for use as light filters, displays, dazzle-freerear view mirrors and the like are known. These involve reversibleelectrochemical oxidation and reduction of redox-active materials suchas tungsten oxide, viologen or various polymers such as polythiophene,polyethylenedioxythiophene (PEDOT), polyaniline inter alia, whichchanges the color thereof. Even though the various known electrochromicsystems work quite well in individual cases, there are also a number ofdisadvantages. The electrochromic materials such as bipyridiniumcompounds (viologens) can be switched between three redox forms,reversibly from the dication to the radical cation and irreversibly tothe uncharged form. In this case, the pimerization of the radicalcations (formation of a Π complex through the Π electron planes) causesan altered absorption spectrum and has an adverse effect on the colorcontrast and the lifetime of the EC systems.

Stabilization materials are required, such as metallocenes andmetallocene derivatives (DE 102007037619A1, US 2009/0259042A1, DE102008024260B4) and also other compounds known, for example, from EP1288275A2 and DE 102006061987, which, by guaranteeing a reversibleanodic component reaction, ensure an improved lifetime of thecathode-switching electrochromic formulation (preferably4,4′-bipyridinium salts) with regard to long-term contrast stability.Here, however, there are likewise problems with regards to colorcontrast and lifetime. In long-term studies, formation of metalloceniumcations becomes perceptible through formation of a yellow-brown layer atthe anode. Moreover, the addition of metallocenes to anelectrochromically active formulation leads to separation processeswhich have been uncontrolled to date, for example the deposition offerrocene aggregates.

Most of the electrochromic materials of significance for applicationsare switchable only between two colors: viologens (colorless

blue/violet), tungsten oxide (WO₃) (light blue

blue), poly-3-hexylthiophene (violet

blue), polyethylenedioxythiophene (PEDOT-PSS) (light blue

dark blue). It is thus possible to implement only two-color filters oronly monochrome displays.

Moreover, many electrochromic materials, for example WO₃ or PEDOT-PSS,are merely pseudo-colorless in thin layers, and so they are only oflimited suitability for the applications where the colorless state isrequired within a broad wavelength range (500-1000 nm).

Numerous studies have been conducted to date with regard to organicmaterials using the electrochromic effect. The great advantage of theelectrochromic polymers and the controllable multichromicity thereofthrough modification of the chemical structure, and the inexpensiveproduction of arbitrarily thin and large-area layers both on glass ormetal substrates and on flexible films and textiles.

Known polymers suitable for electrochromic applications arepolythiophenes, polypyrrole, polyphenylenevinylenes and polyaniline.However, these electrochromic conductive polymers have a tendency toalterations under air, especially with regard to the electricalproperties and electrochemical stability thereof, and as a result haveonly a short lifetime. It is therefore important to encapsulate the ECmodules and to protect them from outside influences. In this context,the necessary rigid encapsulation impairs the flexibility. Moreover,such polymers have a low glass transition temperature, and polypyrroleand polyaniline, for example, have a poor solubility, and so they areprocessable with difficulty. These disadvantages constitute serioushindrances to the practical use thereof.

Particular polymers having di- or triarylamine units are known as holeconductors, electroluminescent materials and light-emitting materials,and also multicolored electrochromes (W. Holzer et al., OpticalMaterials 15, 2000, 225-235).

Examples of the use of diphenylamine and derivatives thereof aselectrochromic material or in combination with anthraquinones aredescribed in U.S. Pat. No. 4,752,119. It has been proposed that asolution of a diphenylamine and a conductive salt in a chemically stableorganic solvent (preferably propylene carbonate) between two electrodesbe used. A TiO₂ scattering layer was applied to an electrode, in orderto better perceive the color change on the white background. As a resultof the application of a voltage of 1.0 V to 1.5 V, the solution takes ona green color. If the voltage is increased to 2.2 V, a blue-green colorforms in the solution. If the voltage is switched off, the systemreturns to the colorless ground state via diffusion. After 10⁶ switchingcycles, only relatively small electrochromic deteriorations in the cellwere registered. However, such systems comprising liquid media areproblematic in terms of the operating temperatures and lifetime;therefore, they have to be hermetically encapsulated.

The invention according to DE 3717917 relates to a novel polymer whichconsists of repeat units of N,N,N′,N′-tetraphenyl-p-phenylenediamine andhas electrochromic properties. The polymer is soluble in organicsolvents and only becomes insoluble once it has been doped with anelectron acceptor and then dedoped. This polymer film shows a yellowcolor in the potential region of 0.3 V (with respect to Ag/AgCl), agreen color in the oxidized state of the first stage at 0.85 V, and adark blue color in the oxidized state of the second stage at 1.2 V. Anelectrochromic display was produced through the following steps: atransparent glass plate was subjected to vapor deposition of aninsulation film of MgF₂ (80 nm) outside the display region, then coatedwith the abovementioned polymer from a chloroform solution (200 nm),subsequently doped with iodine at 100° C. and then dedoped under highvacuum. On another glass plate coated with a graphite fiber layer, aPrussian blue film (300 nm) was electrolytically deposited. Between thetwo glass sheets was disposed a porous background panel made fromalumina, and the two electrodes were sealed. The electrolyte used was 1mol/l solution of LiClO₄ in propylene carbonate. This electrochromicdisplay was switched repeatedly up to 10⁵ times by applying a coloringvoltage of 8 V and a lightening voltage of −8 V. In the course of this,only a small change in the amount of charge was determined in theoxidation reaction compared to the starting value. The production of theelectrochromic display is a multistage operation, combined with variousdifferent technological operations (doping with iodine at 100° C.,dedoping under high vacuum, electrolytic deposition of Prussian blue),which leads to increased technical complexity and investment.Furthermore, the coloring and lightening voltages of ±8 V are very highcompared to conventional EC cells and are economically disadvantageous.

DE 3615379 A1 describes a dazzle-free mirror. The first electrochromiclayer is formed from a conjugated polymer such as a substituted orunsubstituted triphenylamine, and the other EC layer is a transitionmetal oxide, such as WO₃. In the process described, a film is applied tothe electrode from suitable triphenylamine monomer or polymer solutionsusing a coating process and is subsequently polymerized or crosslinkedby means of oxidizing agents, such as iodine, antimony pentafluoride,arsenic pentafluoride or iron oxide. A further means of film formationis an electrolytic polymerization from monomer solution. For example,such a mirror consists of 4,4′-dichlorotriphenylamine polymer and WO₃ EClayers with an electrolyte solution of LiClO₄ in propylene carbonatewith 3% by weight of water. The reflection of the mirror in the groundstate is about 70%. In the case of application of a voltage of about1.45 V, the mirror turns dark blue within about 4 s, and so thereflection is lowered to about 10%. A voltage of about −0.35 V led todecoloring of the mirror. The subsequent coloring (1.1 V, 15 s) anddecoloring (−0.4 V, 90 s) were stably reproducible even after 30 000repetitions. The in situ polymerization or crosslinking of the coatingfilm has the disadvantage that residues of the oxidizing agent in thefilm can lead to unwanted side reactions in the case of repeatedoxidation and reduction, and as a result to an unsatisfactory lifetimeof the device. Equally, it gives an additional methodological step forpractical use.

Electron-rich triphenylamines have a tendency to be oxidized in thepresence of oxygen and light to form an unstable radical cation, whichdimerizes further to a tetraphenylbenzidine. This oxidation leads bothto yellowing of the polymer layers and to a limitation in the lifetimeof the EC elements. By exchange of a group in the para-phenyl position,the dimerization reaction can be significantly reduced. However, it hasbeen published recently that the conjugated homopolymerpoly(4-methoxytriphenylamine) has only a moderately stable EC effect upto about 50 cycles (G.-S. Liou et al., Journal of Polymer Science: PartA: Polymer Chemistry, (2007), V. 45, 3292-3302).

Preparation and basic electrochemical properties of polymers havingaryl-substituted arylenediamine polymers are present in DE 19832943. Ithas been found that the electrooxidation of a solution of a3,3′-substituted triphenyldiamine dimer polymer (TPD polymer) reversiblygives rise to a blue color.

It is desirable to use TPD and tetraarylbenzidine polymers aselectrochromic materials in an electrochromic module with suitableelectrolyte and a suitable ion storage layer, which ensures theperformance of redox reactions with favorable cyclic periodicity andhence a stable EC effect.

SUMMARY OF ADVANTAGEOUS EMBODIMENTS OF THE INVENTION

It is an object of the invention to provide an electrochromic modulewhich is perfectly colorless within a broad wavelength range (500-1100nm) and, in contrast to the prior art, can be produced in fewtechnologically simple, environmentally friendly and inexpensive steps.In addition, it is an object of the invention to display more than twocolor states with only one electrochromic material and, at the sametime, to achieve a large number of switching cycles without anysignificant decline in the electrochromic properties, a highelectrochromic contrast and a high electrochromic efficiency of themodules with effective switching kinetics.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of an exemplary electrochromic (“EC”)module with a multilayer structure;

FIG. 2 is a schematic illustration of an alternative exemplary EC modulewith a multilayer structure;

FIG. 3 is an exemplary electrical circuit diagram of an EC module;

FIG. 4 is a cyclic voltammogram of an exemplary EC module;

FIG. 5 is a spectral transmission of an exemplary EC module in threedifferent switching states;

FIG. 6 is a plot of electrical current against time in an exemplary ECmodule during switching operations:

FIG. 7 is a plot of electrical current against time in an exemplary ECmodule during a switching operation: and

FIG. 8 is a time-dependent transmission during a switching operation.

DETAILED DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS OF THE INVENTION

The object is achieved by an electrochromic module comprising a firstsubstrate, a second substrate, the first and/or second substrate beingelectrically conductive or having been provided with, respectively, afirst electrically conductive coating or with a second electricallyconductive coating, a coating of an electrochromic polymer disposed onthe first substrate or the first conductive coating, an ion storagelayer disposed on the second substrate or the second conductive coatingand an electrically series-connected electrolyte disposed between theelectrochromic coating and the ion storage layer, characterized in thatthe electrochromic polymer is an essentially linear condensation polymerwhich has been formed from a tetraarylbenzidine and a (hetero)aromaticdiol and can be switched reversibly under voltage control between morethan two redox states, the condensation polymer being colorless in oneredox state and colored in at least two redox states, and in that theelectrolyte (7) is a polymeric gel electrolyte.

In the context of the present invention, the first substrate, which isoptionally equipped with a first conductive coating, and theelectrochromic coating disposed on the first substrate or on the firstconductive coating are also referred to collectively as the workingelectrode. Analogously to this, the second substrate, which isoptionally equipped with a second conductive coating, and the ionstorage layer disposed on the second substrate or on the secondconductive coating are also referred to collectively as thecounterelectrode.

The invention proceeds from the known structure of electrochromicmodules, and the electrochromic properties of the inventive polymers incombination with a polymeric gel electrolyte and an ion storage layerare described.

The polymer, which is redox-stable in accordance with the invention, isa tetraarylbenzidine-diol condensation polymer, preferably a copolymerof the following general structural formula I, II, III or IV:

where R1 and R2 are the same or different and are each an alkoxy group,a halogen atom, a cyano group or a hydrocarbyl radical having 1-10carbon atoms, preferably an alkyl group, an allyl group or vinyl group,and R3 is various aromatic radicals. R3 therein is a derivative ofaromatic or heteroaromatic compounds, preferably of benzene,hydroquinone dialkyl ethers, diphenyl ether, biphenyl, naphthalene andother aromatics and heteroaromatics, and compounds thereof.

These polymer films are perfectly colorless and (in the visible lightregion) transparent in the uncharged state and can be colored anddecolored again by a relatively low voltage.

The fact that the polymers used in this application (in one redox state)are colorless is a great advantage over known EC polymers(polythiophenes, polypyrroles, polyphenylenevinylenes, polyaniline andPEDOT-PSS), which are colored both in the oxidized and reduced states.For many applications in which transparency of the device isrequired/desired outside the colored states (including displays,glazing, spectacles), they are therefore perfectly suited.

The inventive polymers have essentially a linear structure and a highglass transition temperature (T_(g)>200° C.). It is advantageous thatthe polymers are stable under air in the form of thin films and do notrequire any inert conditions in the course of processing. Moreover, theyhave good solubility in solvents such as dioxane, chloroform,dichloromethane, chlorobenzene and toluene, as a result of which it ispossible to produce arbitrarily thin layers from solutions on glass ormetal substrates, or else on flexible films and textiles, by means ofspin-coaters, doctor blade technology, roll-to-roll and printingprocesses, and spraying methods, the layer thicknesses being between 50nm and 1 μm, preferably 200 to 500 nm. In contrast to the prior art, theinventive polymer layers do not require any after treatment(crosslinking, polymerizing, doping, dedoping), as a result of which thetechnological procedure is significantly simplified. At the same time,however, they are insoluble in water, alcohols, aliphatic hydrocarbons,propylene carbonate, ionic liquids, for example ethylmethylimidazoliumbis(trifluoromethylsulfonyl)imide (EMITf₂N) and in1-ethyl-3-methylimidazolium tetrafluoroborate, which can be used aselectrolyte in electrochromic modules.

According to the invention, the EC polymers form homogeneous thin layers(approx. 200-500 nm) from solutions having a polymer content of 0.5 to30 percent by mass, preferably of 1 to 3 percent by mass, on differentglasses and flexible substrates, which attain an efficiency in the ECmodule of up to 950 cm²/C and an optical contrast up to 55% for the bluecolor.

The inventive polymers are oxidized into an electrochromic module incombination with a polymeric gel electrolyte (for example based onEMITf₂N) and an ion storage layer on application of a voltage of about0.4 V at the working electrode, as a result of which the module takes ona homogeneous orange color. Moreover, the further oxidation of the ECpolymer on application of a voltage of 0.9 V in the EC module gives riseto a homogeneous blue color. In this case, the orange color state ispassed through. When the voltage decreases down to −1.0 V, the EC modulereturns to the colorless state. More particularly, the inventionprovides EC modules comprising abovementioned polymers, which can beswitched as desired between colorless-clear and colored (e.g.colorless/orange and/or colorless/blue) and between two colors (e.g.orange/blue), or else between three states (colorless/orange/blue).

Because of the optimal combination of EC polymer used, polymeric gelelectrolyte and the ion storage layer, the inventive electrochromicmodules exhibit very good switching kinetics from blue to colorless in 2sec (optical contrast 88%) and from colorless to blue in 7 sec (opticalcontrast 90%, area 3.5 cm²).

In addition, the EC polymers, on application of a voltage of about 0.4V, have a broad long-wave absorption maximum (λ=1300 nm) with an opticalcontrast of about 14%.

Inventive EC modules comprising EC polymers in combination with apolymeric gel electrolyte based on EMITf₂N and an ion storage layerexhibit a stable EC effect above at least 10 000 and preferably at least20 000 colorless/blue switching cycles.

In the invention, a gel-type or polymer-based electrolyte comprising adissolved lithium salt is used. Gel-forming polymers are, for example,poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP),polyacrylonitrile (PAN) or poly(methyl methacrylate) (PMMA). Preferredsolvents are ionic liquids such as 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide (EMITf₂N). Other nonexclusive examplesof solvents are propylene carbonate, mixtures of propylenecarbonate/ethylene carbonate/diethyl carbonate and other carbonates. Inaddition, the polymer-based electrolyte contains, in a concentration of0.1 mol/l to 1 mol/l, a lithium salt such as LiTf₂N, LiTfO (lithiumtrifluoromethanesulfonate) or LiClO₄ (lithium perchlorate). Theconductive salt and gel-forming polymer are fully dissolved in theelectrolyte and thus do not cause any coloring of the electrolyte. Aswell as a high conductivity (up to 6 mS/cm (EMITf₂N, LiTf₂N, PVDF-HFP)),the gel electrolyte particularly has good optical transparency in thevisual range.

In a preferred embodiment of the invention, the counter-electrodecomprises an ion storage layer which to an extent of more than 50% byweight, preferably more than 60% by weight, of a material selected fromthe group consisting of tungsten oxide, nickel oxide, cerium oxide,titanium oxide, molybdenum oxide, vanadium oxide (WO₃, NiO, CeO₂, Ti₂,MoO₃, V₂O₅) and mixtures thereof. Ion storage layers based on CeO₂—TiO₂mixed oxides, which are based on the principle of Li⁺ insertion intoCeO₂, are particularly preferred. Their main task is to rapidly andfully compensate for the charge shifted to the working electrode. Aconventional CeO₂—TiO₂ mixed oxide electrode having a charge storagedensity up to 26 mC/cm₂ using a sol-gel process was used, this alreadyhaving been described in the literature [C. O. Avellane-da et al., ThinSolid Films 471, (2005) 100-104, A. Verma et al., Thin Solid Films 516,(2008) 4925-4933].

The invention is illustrated in detail hereinafter by figures. Thefigures show:

FIGS. 1-2 each an electrochromic module with multilayer structure;

FIG. 3 the electrical circuit diagram of an electrochromic module;

FIG. 4 a cyclic voltammogram of an electrochromic module;

FIG. 5 the spectral transmission of an electrochromic module in threedifferent switching states;

FIGS. 6-7 the plot of electrical current against time in anelectrochromic module during switching operations; and

FIG. 8 the time-dependent transmission during a switching operation.

FIG. 1 shows an inventive electrochromic module 10 with a firstsubstrate 1 and a second substrate 4. The first substrate 1 and thesecond substrate 4 may each consist of a transparent material, such asfloat glass, quartz glass, a polymer film, a metal foil, or atransparent, semitransparent or nontransparent textile. The secondsubstrate 4 may also consist of a nontransparent polymeric, ceramic,metallic or textile material. Preferably, the first and/or secondsubstrate (1, 4) are each provided with a conductive coating, 2 and 5respectively, formed from the same or different materials. Theconductive coatings 2 and 5 consist, for example, of a transparentconductive oxide (TCO) such as tin oxide or zinc oxide, aluminum-dopedtin oxide (ZAO), indium tin oxide (ITO) or fluorine-doped tin oxide(FTO), a metal, for example gold, platinum or stainless steel, or aconductive polymer, for example poly-3,4-ethylenedioxythiophenepoly(styrenesulfonate) (PEDOT-PSS). In alternative embodiments of theinvention, the first substrate 1 and/or the second substrate 4 consistsof an intrinsically conductive textile comprising metallic or metalizedfilaments. In the case of use of a substrate 1 and/or 4 made from anintrinsically conductive textile, there is no conductive coating 2 or 5.

On the substrate 1 optionally equipped with the conductive coating 2 isdisposed a coating 3 consisting of the above-described electrochromicpolymer, i.e. of an essentially linear condensation polymer formed froma tetraarylbenzidine and a (hetero)aromatic diol. The coating 3 isproduced by applying a solution of the electrochromic polymer by meansof known methods, such as spraying, doctor blade coating orspin-coating, to the substrate 1 or to the conductive coating 2.

On the substrate 4 optionally equipped with the conductive coating 5 isdisposed an ion storage layer 6 consisting to an extent of more than 50%by weight, preferably more than 80% by weight, of a material selectedfrom the group comprising cerium oxide, titanium oxide, tungsten oxide,nickel oxide, molybdenum oxide, vanadium oxide (CeO₂, TiO₂, WO₃, NiO,MoO₃, V₂O₅) and mixtures thereof, and more preferably from CeO₂—TiO₂mixed oxide. The ion storage layer 6 is preferably produced by applyinga dispersion of one of the oxides mentioned and subsequently drying andoptionally sintering. Alternatively, the ion storage layer 6 is producedby deposition from the vapor phase, for example by means of CVD or PVD.

The electrochromic module 10 further comprises a polymeric gelelectrolyte 7 which is disposed between the electrochromic coating 3 andthe ion storage layer 6 and comprises at least one crosslinked polymersuch as PVDF-HFP, PAN or PMMA, at least one ionic liquid such as1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide,propylene carbonate, mixtures of propylene carbonate/ethylenecarbonate/diethyl carbonate and at least one lithium salt such asLiTf₂N, LiTfO or LiClO₄.

According to the invention, the polymeric gel electrolyte 7 is disposedbetween the electrochromic coating 3 and the ion storage layer 6 suchthat the electrochromic coating 3, the polymeric gel electrolyte 7 andthe ion storage layer 6 are electrically connected in series (see FIG.3). Accordingly, also envisaged are electrochromic modules in which thesubstrate 1 and/or the substrate 4 consists of an intrinsicallyelectrically conductive textile material, or one which has been equippedwith a conductive coating 2 and/or 5, the polymeric gel electrolyte 7penetrating and filling the pores of the substrate 1 and/or 4 andencasing the conductive filaments thereof.

Optionally, the electrochromic module 10 is equipped on the edge sidewith a seal 8. The seal 8 consists, for example, of a polymeric materialand surrounds the edge of the layer of the polymeric gel electrolyte 7.The seal preferably extends partly or fully over the edges of thesubstrates 1 and 4.

FIG. 2 shows a further electrochromic module 20 according to the presentinvention. The module 20 comprises a structured conductive coating 2Aand/or a structured conductive coating 5A. In appropriateconfigurations, in addition, a structured electrochromic coating 3Aand/or a structured conductive ion storage layer 6A are provided. Theterm “structured layer” or “structured coating” in the context of theinvention refers to a circuitry pattern produced by means of knownmethods, such as photolithography. More particularly, matrix-likepatterns are provided, which enable operation of the electrochromicmodule 20 in the manner of a display and utilization for the digitallycontrolled display of images and symbols.

The example which follows illustrates the production of an inventiveelectrochromic module.

Example 1

A toluene solution containing 1.5 percent by mass of polymer, preparedby polycondensation of 1,4-bis(phenylhydroxymethyl)benzene andN,N′-bis(4-methylphenyl)-N,N′-diphenylbenzidine is applied to an FTOglass (i.e. glass equipped with an electrically conductive coatingcomposed of fluorine-doped tin oxide) by means of a spin-coater, forminga homogeneous film of thickness about 500 nm (after drying). This isenvisaged as the working electrode (WE) in the EC module. An ethanolicsolution containing 5% by mass of water, 0.2 mol/l of ammonium cerium(IV) nitrate (NH₄)₂Ce(NO₃)₃ and 0.2 mol/l of tetraisopropylorthotitanate (Ti(o-propyl)₄) is applied to the other FTO glass by meansof a spin-coater in a thin layer, and dried at 150° C. This is repeatedthree times and the whole assembly is finally heated at 500° C., forminga CeO₂—TiO₂ mixed oxide. This is then used in the EC modules as thetransparent counterelectrode (CE). Two coated FTO glasses (WE and CE)are then combined to give the EC module by means of a heat-sealing film.The EC module is finally filled in a glovebox with polymer electrolyte(PVDF-HFP, LiTf₂N 0.1 mol/l in EMITf₂N) at 90° C. through two smallholes, and the latter are subsequently sealed.

The cyclic voltammogram of a reversible electrochemical oxidation of theEC polymer in combination with polymer electrolyte (PVDF-HFP, LiTf₂N 0.1mol/l in EMITf₂N), demonstrated in an EC module produced according toexample 1, is shown in FIG. 4 (measuring instrument: Solartron 1285, 15mV/S). The UV-VIS transmission spectra of the same EC module in thecolorless state and on application of a voltage of +0.4 V (orange) andof +0.9 V (blue) are shown in FIG. 5 (measuring instrument: Unicam UV300, measured against air). Chronoamperometry measurements for theswitching operations between the potentials of −1.0 V and +0.4 V(colorless-orange) and −1.0 V and +0.9 V (colorless-blue) are shown inFIG. 6 and FIG. 7. Here, very small current densities of 0.2-0.6 mA/cm²are observed directly after a potential switch. The switching times areobtained from time-dependent electro-optical measurements on the ECmodule, produced according to example 1, for colorless/blue switchingoperations (λ=750 nm) (see FIG. 8). Tab. 1 summarizes the electrochromiccharacteristics of the modules according to example 1 for orange andblue coloring.

The optical contrast is defined as the transmission difference betweentwo (color) states at a particular wavelength. In our case, this is thetransmission difference between the transparent ground state and theorange or blue states. The transmission of the EC module was measuredwith a Unicam UV 300 UV-VIS spectrometer against air (reference) at roomtemperature. The transmission is defined as the ratio of the intensityof the light beam transmitted through the electrochromic module to theintensity of the incident light beam in percent.

TABLE 1 Electrochromic properties of the module produced according toexample 1. Orange Blue Characteristic (λ = 480 nm) (λ = 750 nm)Electrochromic contrast, 29% 54% Δ% T Optical density OD = log 0.2740.61 (T_(bleaching)/T_(coloring)) Charge density, Q, (C/cm²) 2.9E−42.1E−3 Electrochromic efficiency 945 290 (280*, (cm²/C), η = log OD/Q300**) *after 4200 colorless/blue switching operations **after 10 000colorless/blue switching operations

The invention claimed is:
 1. An electrochromic module comprising a firstsubstrate, a second substrate, the first and/or second substrate beingeither electrically conductive or having been provided with anelectrically conductive coating, a coating of an electrochromic polymerdisposed on the substrate or the conductive coating, an ion storagelayer disposed on the substrate or the conductive coating and anelectrically series-connected electrolyte disposed between theelectrochromic coating and the ion storage layer, wherein theelectrochromic polymer is an essentially linear condensation polymerwhich has been formed from a tetraarylbenzidine and a (hetero)aromaticdiol and can be switched reversibly under voltage control between morethan two redox states, the condensation polymer being colorless in oneredox state and colored in at least two redox states, and theelectrolyte is a polymeric gel electrolyte.
 2. The electrochromic moduleas claimed in claim 1, wherein the electrochromic polymer is anessentially linear condensation polymer formed from a substitutedtetraphenylbenzidine and a (hetero)arylenebisphenylmethanol of thegeneral structural formula (I), (II), (III) or (IV)

where R1 and R2 are the same or different and are each an alkoxy group,a halogen atom, a cyano group or a hydrocarbyl radical having 1-10carbon atoms, and R3 is a divalent radical of an optionally substitutedaromatic or heteroaromatic compound.
 3. The electrochromic module asclaimed in claim 1, wherein the electrochromic polymer has a glasstransition temperature Tg of more than 200° C.
 4. The electrochromicmodule as claimed in claim 1, wherein the polymeric gel electrolytecomprises at least one crosslinked polymer, at least one ionic liquidand at least one lithium salt.
 5. The electrochromic module as claimedin claim 1, wherein the ion storage layer comprises more than 50% byweight of a material selected from the group comprising tungsten oxide,nickel oxide, cerium oxide, titanium oxide, molybdenum oxide, vanadiumoxide and mixtures thereof.
 6. The electrochromic module as claimed inclaim 1, wherein the electrochromic polymer is switched under voltagecontrol between three redox states.
 7. The electrochromic module asclaimed in claim 1, wherein on application of a voltage in the rangefrom 0.35 to 0.45 V said electrochromic module has a broad absorptionband having an absorption maximum in the wavelength range from 1200 to1400 nm, and an optical contrast in the absorption maximum of from 13%to 15%.
 8. The electrochromic module as claimed in claim 1, wherein theelectrochromic module has a number of switching cycles with a contrastin the range from 90 to 100%, based on a starting value, of greater than20
 000. 9. The electrochromic module as claimed in claim 1, wherein saidelectrochromic module has an electrochromic efficiency of greater than600 cm²/C.
 10. The electrochromic module as claimed in claim 1, whereinsaid electrochromic module has an electrochromic contrast of greaterthan 40%.
 11. The electrochromic module as claimed in claim 1, whereinthe switching time from blue to colorless is less than 2 s and theswitching time from colorless to blue is less than 7 s.
 12. Theelectrochromic module as claimed in claim 1, wherein the electrochromicpolymer forms a homogeneous layer having a thickness of 5 to 500 nm. 13.The electrochromic module as claimed in claim 2, wherein the carbonatoms are an alkyl group, an allyl group or a vinyl group and thearomatic or heteroaromatic compound is benzene, a hydroquinone dialkylether, diphenyl ether, biphenyl or naphthalene.
 14. The electrochromicmodule as claimed in claim 4, wherein the crosslinked polymer isPVDF-HFP, PAN or PMMA, the ionic liquid is 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide, propylene carbonate, or a propylenecarbonate/ethylene carbonate/diethyl carbonate mixture and the lithiumsalt is LiTf₂N, LiTfO or LiClO₄.
 15. The electrochromic module asclaimed in claim 5, wherein the ion storage layer comprises more than80% by weight of CeO₂—TiO₂ mixed oxide.
 16. The electrochromic module asclaimed in claim 6, wherein the electrochromic polymer, according to theredox state, assumes the color states of colorless, orange or blue. 17.The electrochromic module as claimed in claim 9, wherein theelectrochromic efficiency is greater than 800 cm²/C.
 18. Theelectrochromic module as claimed in claim 10, wherein the electrochromiccontrast is greater than 60%.
 19. The electrochromic module as claimedin claim 12, wherein the homogeneous layer has a thickness of 50 to 500nm.
 20. The electrochromic module as claimed in claim 12, wherein thehomogeneous layer has a thickness of 200 to 500 nm.